ra_serf: Guard against SERF_VERSION_AT_LEAST(unreleased version) logic.

Before this change, our code contained several blocks of code conditional
on SERF_VERSION_AT_LEAST(1, 4, 0).  Since Serf 1.4.0 is unreleased, this
code relies on development snapshots rather than a stable API.

Essentially, that's a ticking timebomb.  The code encodes assumptions
about a development version of Serf but will automatically activate if
a user builds against an officially released Serf 1.4.0+.

More specifically:

- The code may not compile, depending on the final API state in Serf 1.4.0+.
- Even if it compiles, assumptions about Serf's behavior may no longer hold.
- Even if the assumptions hold, these code paths may still not work as intended,
  because they are effectively hidden from our standard release testing and
  buildbots.

To fix this issue, place such code under an additional guard (#ifdef
SVN__SERF_EXPERIMENTAL) that is never defined in production builds.

See [1] for additional details.

* subversion/libsvn_ra_serf/serf.c
  (load_config): Guard code with #ifdef SVN__SERF_EXPERIMENTAL.

* subversion/libsvn_ra_serf/update.c
  (get_best_connection): Guard code with #ifdef SVN__SERF_EXPERIMENTAL.

* subversion/libsvn_ra_serf/util.c
  (conn_negotiate_protocol, conn_setup, svn_ra_serf__default_readline):
   Guard code with #ifdef SVN__SERF_EXPERIMENTAL.

[1]: https://lists.apache.org/thread/7dpmb63wc1phqvgwvp9hnyrzfqpd2mz5


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1930808 13f79535-47bb-0310-9956-ffa450edef68

Author: evgenykotkov

subversion/libsvn_ra_serf/serf.c

@@ -165,9 +165,11 @@ load_config(svn_ra_serf__session_t *session,
   const char *exceptions;
   apr_port_t proxy_port;
   svn_tristate_t chunked_requests;
+#ifdef SVN__SERF_EXPERIMENTAL
 #if SERF_VERSION_AT_LEAST(1, 4, 0) && !defined(SVN_SERF_NO_LOGGING)
   apr_int64_t log_components;
   apr_int64_t log_level;
+#endif
 #endif
 
   if (config_hash)
@@ -252,6 +254,7 @@ load_config(svn_ra_serf__session_t *session,
                                   SVN_CONFIG_OPTION_HTTP_CHUNKED_REQUESTS,
                                   "auto", svn_tristate_unknown));
 
+#ifdef SVN__SERF_EXPERIMENTAL
 #if SERF_VERSION_AT_LEAST(1, 4, 0) && !defined(SVN_SERF_NO_LOGGING)
   SVN_ERR(svn_config_get_int64(config, &log_components,
                                SVN_CONFIG_SECTION_GLOBAL,
@@ -261,6 +264,7 @@ load_config(svn_ra_serf__session_t *session,
                                SVN_CONFIG_SECTION_GLOBAL,
                                SVN_CONFIG_OPTION_SERF_LOG_LEVEL,
                                SERF_LOG_INFO));
+#endif
 #endif
 
   server_group = svn_auth_get_parameter(session->auth_baton,
@@ -319,6 +323,7 @@ load_config(svn_ra_serf__session_t *session,
                                       SVN_CONFIG_OPTION_HTTP_CHUNKED_REQUESTS,
                                       "auto", chunked_requests));
 
+#ifdef SVN__SERF_EXPERIMENTAL
 #if SERF_VERSION_AT_LEAST(1, 4, 0) && !defined(SVN_SERF_NO_LOGGING)
       SVN_ERR(svn_config_get_int64(config, &log_components,
                                    server_group,
@@ -328,9 +333,11 @@ load_config(svn_ra_serf__session_t *session,
                                     server_group,
                                     SVN_CONFIG_OPTION_SERF_LOG_LEVEL,
                                     log_level));
+#endif
 #endif
     }
 
+#ifdef SVN__SERF_EXPERIMENTAL
 #if SERF_VERSION_AT_LEAST(1, 4, 0) && !defined(SVN_SERF_NO_LOGGING)
   if (log_components != SERF_LOGCOMP_NONE)
     {
@@ -348,6 +355,7 @@ load_config(svn_ra_serf__session_t *session,
       if (!status)
           serf_logging_add_output(session->context, output);
     }
+#endif
 #endif
 
   /* Don't allow the http-max-connections value to be larger than our

subversion/libsvn_ra_serf/update.c

@@ -616,7 +616,7 @@ get_best_connection(report_context_t *ctx)
     }
   else
     {
-#if SERF_VERSION_AT_LEAST(1, 4, 0)
+#if defined(SVN__SERF_EXPERIMENTAL) && SERF_VERSION_AT_LEAST(1, 4, 0)
       /* Often one connection is slower than others, e.g. because the server
          process/thread has to do more work for the particular set of requests.
          In the worst case, when REQUEST_COUNT_TO_RESUME requests are queued

subversion/libsvn_ra_serf/util.c

@@ -481,6 +481,7 @@ load_authorities(svn_ra_serf__connection_t *conn, const char *authorities,
   return SVN_NO_ERROR;
 }
 
+#ifdef SVN__SERF_EXPERIMENTAL
 #if SERF_VERSION_AT_LEAST(1, 4, 0) && defined(SVN__SERF_TEST_HTTP2)
 /* Implements serf_ssl_protocol_result_cb_t */
 static apr_status_t
@@ -512,6 +513,7 @@ conn_negotiate_protocol(void *data,
   return APR_SUCCESS;
 }
 #endif
+#endif
 
 static svn_error_t *
 conn_setup(apr_socket_t *sock,
@@ -558,6 +560,7 @@ conn_setup(apr_socket_t *sock,
               SVN_ERR(load_authorities(conn, conn->session->ssl_authorities,
                                        conn->session->pool));
             }
+#ifdef SVN__SERF_EXPERIMENTAL
 #if SERF_VERSION_AT_LEAST(1, 4, 0) && defined(SVN__SERF_TEST_HTTP2)
           if (APR_SUCCESS ==
                 serf_ssl_negotiate_protocol(conn->ssl_context, "h2,http/1.1",
@@ -567,6 +570,7 @@ conn_setup(apr_socket_t *sock,
                             conn->conn,
                             SERF_CONNECTION_FRAMING_TYPE_NONE);
             }
+#endif
 #endif
         }
 
@@ -2273,7 +2277,7 @@ svn_ra_serf__default_readline(serf_bucket_t *bucket, int acceptable,
                               int *found,
                               const char **data, apr_size_t *len)
 {
-#if SERF_VERSION_AT_LEAST(1, 4, 0)
+#if defined(SVN__SERF_EXPERIMENTAL) && SERF_VERSION_AT_LEAST(1, 4, 0)
   return serf_default_readline(bucket, acceptable, found, data, len);
 #else
   return bucket_limited_readline(bucket, acceptable, SERF_READ_ALL_AVAIL,